Traditional metal halide (MH) lamps use probe-start technology.
Three electrodes are present in the arc tube of a probe-start
MH lamp: a starting probe electrode and two operating electrodes
. To start the lamp, a discharge is created across
a small gap between the starting probe electrode (also called
the starter electrode) and the operating electrode. Electrons
then jump across the arc tube to the other operating electrode
to help start the lamp. Once the lamp is started, a bi-metal
switch removes the starting probe electrode from the circuit.
Each time a MH lamp is turned on, tungsten sputters from the
electrodes. Over the lamp life, this tungsten can cause the
arc tube wall to blacken, thus reducing performance of the lamp.
Pulse-start MH lamps do not have the starting probe electrode
. Instead they have a high-voltage ignitor that works
with the ballast to start the lamp using a series of high-voltage
pulses (typically 3 to 5 kilovolts). Without the probe electrode,
the amount of pinch (or seal) area at the end of the arc tube is
reduced, which results in a reduced heat loss. Furthermore, using
an ignitor with a lamp reduces the tungsten sputtering by heating
up the electrodes faster during starting. Warm-up time is also
reduced. Pulse-start technology was developed to increase lamp
life and to have both the energy efficacies of high-pressure
sodium (HPS) lamps and the desirable color characteristics of
MH lamps
Pulse-start technology is not new; it has been available in
low-wattage MH systems for years. Manufacturers claim that
pulse-start systems achieve the following:
Provide longer lamp life of up to 50% over traditional MH lamps.
Increase lumen maintenance by up to 33%
Provide better cold starting capability-these lamp-ballast systems
will start at temperatures as low as -40?C (-40?F)
Allow faster starting when cold, shorter warm-up times, a
nd a faster restrike (re-start).
